The present invention relates to a resist processing method and resist processing apparatus for coating and forming a thin-film, such as a photoresist film, on a substrate such as a semiconductor wafer having an already formed circuit pattern with an uneven/stepped surface.
The photolithography process for manufacturing a semiconductor device includes coating a photoresist solution on the surface of a semiconductor wafer to form a resist film, baking this resist film, exposing the film with light with the use of a pattern and subjecting it to a develop-processing.
In the process of coating the photoresist film, use is made of the so-called spin-coating method by which the wafer, being spun, is supplied at its center surface area with a resist solution and the resist solution is diffused under a centrifugal force over a whole wafer surface. In the case where a resist solution is coated on an uneven/stepped surface of a wafer W with a circuit pattern layer 2 already formed thereon, a thickness tmin of a resist film 3 on a top area 2a becomes extremely smaller than a thickness tmax of the resist film on a bottom area 2b as shown in FIG. 1. If, therefore, in a subsequent light exposure step, the next circuit pattern is subjected to light exposure, there is a risk that there will arise a variation in the width of a light beam. Such a light beam width variation tendency emerges more prominently when the light exposure wavelength becomes short from an i line to a KrF excimer laser.
In recent times, the light beam width of a circuit pattern for the semiconductor device is more and more microminiaturized and there is a high demand that the thickness of the resist film be further reduced.